The paper is the most recent and comprehensive review on enantioselective Michael addition reactions carried out with catalytic amounts of both a transition metal and a chiral ligand. The method is used by many research groups for the stereoselective synthesis of chiral target molecules, in particular natural products and pharmaceutically active compounds. The unique feature of our review is that it covers all important transition metals (copper, nickel, rhodium, lanthanides, etc.) and even pure "organocatalytic" (metal-free) reactions, so that it appeals to many more researchers than other reviews which are specialized to only one metal.

This field is very "hot" right now, and new chiral ligands and procedures for catalytic enantioselective Michael additions appear almost every week. Since the publication of our review, I have collected over 100 new papers in the field! The most important advantage of the method (from my point of view) is that it can be used reliably for the synthesis of new, previously unknown products—even by "outsiders" who do not have any knowledge of the subtleties of the catalytic systems. Just a few years ago, a tedious screening of ligands and reaction conditions had to be carried out for every new substrate.

We are specialists in the use of organocopper compounds in organic synthesis, and have recently begun to use copper-catalyzed enantioselective Michael additions. Consequently, we know the literature concerning copper as catalyst metal rather well, and it was fascinating to learn how many interesting methods have recently been developed by using other transition metals. We will now also start to use also rhodium-catalyzed enantioselective Michael additions in our own research.

Many highly active drugs exist in two forms: object and mirror image. Usually, the human organism interacts differently with these two forms ("enantiomers"); one has the desired pharmacological activity, whereas the other is inactive or even harmful. A nice comparison is the human hand: a right glove does only fit to the right hand, not to the left. For this reason, it is very important to develop methods that allow for the synthesis of one enantiomer of these target molecules only ("enantioselective reaction"). The "Michael reaction" (named after the American chemist Arthur Michael) can be used towards this purpose, but only when being carried out in the presence of a transition metal (for example copper) and another molecule (chiral ligand). For economical and environmental reasons, it is highly desirable to use only very small amounts of these auxiliaries; such reactions are called "catalytic". Thus, the catalytic enantioselective Michael addition is ideal for the synthesis of drugs and other important target molecules.